Aflatoxin is one of the most potent carcinogens among those hitherto known. Aflatoxin is a metabolite secreted by the aflatoxin-producing fungi such as Aspergillus flavus and Aspergillus parasiticus, and several homologues thereof including aflatoxin B.sub.1 and aflatoxin G.sub.1 are also known.
Among food cereals such as wheat, barley, rice, corn (maize), etc. and food nuts such as hazelnut, almond, Brazil nut, peanut, etc., those contaminated with the aflatoxin have been found (cf. Am. Assoc. Cereal Chemists Inc., 595(1974); Am. Assoc. Cereal Chemists Inc., 603(1975); JAOCS, 980A, December (1981); J. Agric. Food Chem., 26, 249 (1978); Dtsch Lebensm. Rudsch., 76, 47(1980); Lebensm. -Wiss. u. -Technol., 14, 252(1981)), and the aflatoxin-producing fungous microbes are supposed to possibly spread around the areas where these crops are cultivated and yielded. Since such cereals and nuts contaminated with the aflatoxin provide a serious health problem, a lot of countries strictly regulate the importation of the contaminated cereals and nuts so as not to enter their territories.
When the cereals and nuts are grown in a field infected with the aflatoxin-producing fungi, the possibility that the yielded cereals and nuts are as well contaminated with the aflatoxin is likely very high. Particularly, in tropical and subtropical zones quite many fields have been found to be infected and contaminated with those aflatoxin-producing fungi. It is an urgent measure to prevent the aflatoxin contamination in the cereals and nuts and to provide the cereals and nuts free from those carcinogenic aflatoxin.
It is known that the aflatoxin may be removed in soil (cf. Soil Sci. Soc. Am. J., 44, 1237 (1980)), and the adsorption of the aflatoxin to the soil and the participation of some microbes in the removal of the aflatoxin are supposed to be causes therefor. Further, it has been reported that many microbes may experimentally reduce the quantity of aflatoxin in an aqueous test solution into which the aflatoxin is dissolved (cf. J. Bact., 93, 464 (1967); J. gen. Microbiol., 54, 185 (1968); Naturwissenschaften, 62, 537 (1975); Proc. Japan. Assoc. Mycotoxicol., 12, 33 (1980)). Among those microbes, Flavobacterium aurantiacum, Bacillus megaterium, Corynebacterium rubrum, Penicillium islandicum, Stachybotrys lobulata, Cumminghamella echinulata, Streptococcus lactis and so on have hitherto been informed as the microbes moderately eliminating the aflatoxin in the test solution.
However, many of the reductions of aflatoxin by the microbes hereinabove mentioned are caused due to the adsorption of the aflatoxin to cell walls of the microbes (cf. J. gen. Microbiol., 54, 185 (1968); J. Bacteriol., 93,464(1967)) and besides the removal of the aflatoxin took place in an experimental test solution containing it. Referring to those publications, the removal of the aflatoxin from the cereals and nuts growing in the field and the prevention of the aflatoxin contamination in those cereals and nuts have not yet been actually accomplished by making use of the microbes hereinbefore mentioned.
Moreover, the removal of the aflatoxin from the yielded cereals and nuts may require a large amount of microbes, which is unsuitable for foodstuffs. In addition, it is difficult to completely eliminate the aflatoxin which is present within cores of the cereals and nuts. Besides, it is unknown whether or not these microbes are harmless to human being when applied to the foodstuffs. They possibly include microbes associated with hygienic problems such as pathogenicity. Moreover, there may be a species such as Streptococcus lactis which demands a specific nutritional requirement, and accordingly is unsuitable for treating the food cereals and nuts.
The present inventor has investigated microorganisms present in the soil at various regions in order to develop a method for preventing the contamination of cereals and nuts with the aflatoxin while using a microbe which is safe and harmless to the human being even when applied to the foodstuffs, and as a consequence found strains belonging to Bacillus subtilis which has so far closely been connected to the field of foodstuff industry, which strains can reduce the quantity of the aflatoxin in the aqueous solution as well as inhibit both the growth of the aflatoxin-producing fungi and their production of aflatoxin.
On the other hand, R. Mann et al. (Z. Lebensm. Unters. -Forsch., 163, 39 (1977)) describe that there are strains capable of eliminating the aflatoxin among B. subtilis (ATCC 6633 and ATCC 9372). R. Mann et al. further describe that 40 to 50% of the aflatoxin was reduced in an aflatoxin solution for 20 days. But, at such a degree of reduction, the substantial removal of the aflatoxin from the cereals and nuts growing in the field can not be expected.
D. T. Wicklow et al. (Phytopathology, 70, 761 (1980)) report that Aspergillus flavus may be inhibited in its proliferation and aflatoxin-producing activity under the co-presence of Aspergillus niger or Trichoderma viride. But the microorganisms of the present invention are bacteria, not mold such as in D. T. Wicklow et al.